Although Justin, our most important source for the first century of the Parthian Empire, mentions that Phraates II (the son and successor of the great conqueror Mithradates I the Great) was succeeded in 127 BCE by his uncle Artabanus I,note[Justin, Epitome 42.2.1.] there is sufficient numismatic and documentary evidence (e.g, ostraca from Nisa) that Artabanus succeeded Phraates only after some eight months, after the brief reign of one Bagasis.

It is extremely likely that this Bagasis is identical to an important official whose earlier career is known from other sources:

148 BCE: Justin mentions that king Mithradates, after the conquest of Media, appointed his brother Bacasis as governor.note[Justin, Epitome 41.6.7.]

October 135 BCE: the Astronomical Diaries mention that because Mithradates has suffered a stroke, Bagayasha has been appointed as the king's substitute.note[AD III, p. 194, no. -134B 15’-17’.]

October/November 132 BCE: the Astronomical Diaries refer to religious riots in Babylon and Borsippa. Bagayasha discharges the general of Babylonia, Philinus, from his office. A man named Theodosius is appointed.note[AD III, p. 216, no. –132 B rev. 18ff.] This seems to be the context of the Chronographic Document concerning Bagayasha(BCHP 18).

May/June 120 BCE: the Astronomical Diaries mention a certain [PN x]x-na-a, son of Bagayasha, who is general of Babylonia.note[AD III p. 312, no. –119.]

It seems that the final stage of this splendid career was the kingship, as successor of Mithradates' son Phraates II, but it is frustrating that we have no information about the reign of Bacasis/Bagayasha/Bagasis, except that it lasted for only several months in 127/126 BCE and led to the accession of Artabanus I (r.126-122). From the fact that Bagayasha's son [PN x]x-na-a was to occupy a very high military office in Babylonia during the reign of Mithradates II (r.121-91), we may infer that Bagayasha had not fallen into disgrace and remained highly respected.

Note

The chronology of the Arsacid kings of the Parthian Empire is less well-understood than, for example, the sequence of Seleucid and Ptolemaic kings or the emperors of Rome. This information is based on the researches by G.R.F. Assar, as published in "Iran under the Arsakids, 247 BC – AD 224/227" in: Numismatic Art of Persia (2011).